This invention relates to a novel composition for polyurethane resins and the production of the resins. More particularly, it relates to a multi-pack type composition for polyurethane resins and for ambient temperature curing which comprises an isocyanate component having oxadiazinetrione ring, an active hydrogen component and a Lewis base whose basic site has no hydrogen active to NCO group, and to a process for preparing polyurethane resins from said composition.
Hitherto, polyurethane resins have been used as, for example, coatings, adhesives and elastomers for various substrates such as woods, metals, roofing tiles, concretes, plastics, rubbers, papers floor covering materials, water-proof materials, sealing materials, etc., because they are superior to other synthetic resins in chemical resistance, mechanical properties, stain resistance, adhesiveness, gloss, wear resistance, weathering resistance, etc.
As compositions for the polyurethane resins, one-pack type and multi-pack type such as two-pack type are known. The two-pack type compositions usually comprise an active hydrogen component which is a main component and a polyfunctional polyisocyanate component which is a curing agent. As this curing agent, commonly used are derivatives such as polyisocyanates having urethane, urea or biuret bond obtained by reaction of a diisocyanate as a starting material with a polyol, water, an amine, etc. and polyisocyanates having isocyanurate ring obtained by trimerization of a diisocyanate using catalysts. However, isocyanate content of such derivatives is much lower than that of the starting diisocyanate. Therefore, a considerably larger amount of curing agent is needed than that of the active hydrogen compound, a main component. However, a curing agent is expensive as compared with the main component and such curing agents as capable of curing even in a small amount have been desired. Furthermore, said derivatives are of high viscosity and sometimes they must be diluted with solvents when they are used as a curing agent. Thus, high solid content type or solventless type curing agents have been demanded from point of saving resources and prevention of environmental pollution. Furthermore, urethane resin compositions curable at ambient temperature generally require a long time for complete curing and hence are inferior in workability.
This invention provides useful solventless type polyurethane resin compositions as well as solvent type polyurethane resin compositions. Recently, various coatings, adhesives and elastomer compositions containing no solvent have been proposed. However, these are inferior to solvent type compositions in workability, drying speed, mechanical properties, adhesiveness, etc. Solvent type compositions can be provided with a suitable viscosity by adjusting an amount of solvent added thereto. However, in the case of solventless type compositions, the use of main component of low molecular weight is necessarily demanded for reducing viscosity. Hence, the compositions require a long time for drying and curing, and the resulting cured products also have unsatisfactory properties. The composition of this invention, even in the case of solventless type, is excellent in operability and curable for a short period of time, and the resulting cured products have excellent mechanical properties.
The present inventors have found that the reaction for producing allophanates from oxadiazinetrione ring and active hydrogen compounds readily proceeds even at ambient temperature in the presence of a Lewis base whose basic site has no hydrogen active to NCO group. They have made intensive researches to apply this knowledge to curing of urethane compositions. As a result, it has been found that when an isocyanate component having oxadiazinetrione ring, as a curing agent, is reacted with an active hydrogen component in the presence of a Lewis base whose basic site has no hydrogen active to NCO group in order to prepare coatings, adhesives, elastomers, etc., the amount of the curing agent to be used may be small, the agent can be used as high solid content type or solventless type compositions, and furthermore curability thereof is superior to that of the conventional urethane curing agents. Thus, according to the present invention, the above mentioned problems can be completely solved.